'symbol' is not defined as a preprocessor macro, replacing with '0' for 'directives'
A symbol that was not defined was used with a preprocessor directive. The symbol will evaluate to false. This warning is off by default. To define a symbol, you can use either the #define directive or /D compiler option.
The following sample generates C2668:
#include <stdio.h> #pragma warning (default : 4668) // turn warning on void main() { #if q // q is not defined printf("defined"); #else printf("undefined"); #endif }